1. Field
The invention relates to image detecting arrays, specifically far infrared detectors and non-destructive methods of testing Large Scale Integration (LSI) arrays.
2. Prior Art
A typical prior art technique for characterizing and testing a far-infrared photodiode is shown in the article "Background and temperature dependent current-voltage characteristics of HgCdTe photodiodes" by J. P. Rosbeck, et al. in the Journal of Applied Physics, Vol. 53, No. 9, September 1982, pp 6430-40. The diode is placed on a cold stage (77.degree. K.) and I-V characteristics are measured by an electrometer and other instruments physically contacting the diode. Each measurement is made while the diode is irradiated at a different frequency in the response spectrum of the diode.
So called, first generation arrays of these diodes have expanded from individual diodes to linear arrays containing hundreds of diodes and testing by such methods has become a very tedious process. Fortunately as confidence in manufacturing techniques has increased the amount of testing required has reduced sufficiently to permit mass production. A new array for second generation far-infrared image detectors involves LSI and will be far too sophisticated for this type of testing.
The new array will have thousands rather than hundreds of diodes. The chip will employ solder-bumps to make the HgCdTe structure to a silicon chip with a highly sophisticated charge coupled device (CCD) to extract the information stored by the diodes. Testing would be simpler after the two chips are mated, but then it would be too difficult to disassemble the device and perhaps salvage one of the chips. Testing the array chip alone by the old methods would take 24 hours or more per chip.
The Siemens Company in Germany has developed an E-Beam Tester Model 8410 which performs high-speed no-load testing of intergrated circuit chips (IC's). The device can be used on chips that are passivated by an oxide coating in a non-destructive manner. First generation arrays were provided with extra diodes on which destructive testing could be performed. The Siemens tester is adequate for testing the second generation CCD chip, but can not adequately test the second generation array chips. An object of the present invention is to provide a tester using the E-Beam principle to fully test the latter chip.